This invention relates to electrophoresis generally, and more particularly, to an apparatus and method for performing capillary array electrophoresis on microfabricated structures.
In many diagnostic and gene identification procedures such as gene mapping, gene sequencing and disease diagnosis, deoxyribonucleic acid (DNA), ribonucleic acid (RNA) or proteins are separated according to their physical and chemical properties. In addition to DNA, RNA or proteins, other small molecule analytes may also need to be separated.
One electrochemical separation process is known as electrophoresis. In this process, molecules are transported in a capillary or a channel which is connected to a buffer-filled reservoir. An electric field in the range of kilovolts is applied across both ends of the channel to cause the molecules to migrate. Samples are typically introduced at a high potential end and, under the influence of the electric field, move toward a low potential end of the channel. After migrating through the channel, the separated samples are detected by a suitable detector.
Typically, electrophoretic separation of nucleic acids and proteins is carried out in a gel separation medium. Although slab gels have played a major role in electrophoresis, difficulties exist in preparing uniform gels over a large area, in maintaining reproducibility of the different gels, in loading sample wells, in uniformly cooling the gels, in using large amounts of media, buffers, and samples, and in requiring long run times for extended reading of nucleotides. Moreover, slab gels are not readily amenable to a high degree of multiplexing and automation. Recently, micro-fabricated capillary electrophoresis (CE) devices have been used to separate fluorescent dyes and fluorescently labeled amino acids. Additionally, DNA restriction fragments, polymerase chain reaction (PCR) products, short oligonucleotides and even DNA sequencing fragments have been effectively separated with CE devices. Also, integrated micro-devices have been developed that can perform polymerase chain reaction amplification immediately followed by amplicon sizing, DNA restriction/digestion and subsequent size-based separation, and cells sorting and membrane lysis of selected cells. However, these micro-fabricated devices only perform analysis on one channel at a time. For applications such as population screening or DNA sequencing, such a single channel observation and analysis results in an unacceptable delay for screening many members of a population.